It is difficult to know the size of your satsuma from the photo, but this looks like long-term damage, not just from this winter. Frost damage does cause bark splitting, but you would first see die-back of smaller twigs and tender leaves.
This damage is due to some kind of fungal rot, possibly initially caused by some physical damage or because of too damp conditions allowing attack by the phytophthora fungus.
There appears to be a patch of white goo which could be fungus - clean this away.
If this rot encircles the whole trunk then your tree is dead. What does the other side look like?
There is a product called Aliette which can stop phytophthera rot but may not be available in your area of USA.
I would brush as much of of the growing mix away from the trunk and ensure that the area is kept dry. Keep water away from the trunk and perhaps reduce watering frequency.